The geological and geomorphological value of Ha Long Bay
In 2000, Ha Long Bay was recognised by UNESCO as a world natural heritage site for the second time with outstanding universal geological and geomorphological value.
According to scientists, the appearance of Ha Long Bay - Cat Ba Archipelago and its unique and famous geological and geomorphological values today are the result of a regional tectonic movement that lasted more than 500 million years. The remaining marks of geological evolution and tectonic movements are faults, folds, grabens, ramparts, basins and formations that mark profound changes in the paleogeographical circumstances of the region. Ha Long Bay has undergone countless times of subsidence - sea level rise and mountain building - sea level fall, thus it possesses diverse values for Anthropocene geology and marine geology.
The geological diversity of Ha Long Bay includes the diversity in material composition, architecture, structure and geological evolution, and the diversity in ancient and modern sedimentary environments with special paleogeographic periods that have created the diversity in terrain, geomorphology and natural landscape.
The geomorphological value of Ha Long Bay is the diversity of topographic elements including mountainous islands interspersed with deep sea bays, the contrast of coastal mangrove forests and steep limestone islands. This is the oldest type of terrain still observed in Vietnam. In the mainland and islands, erosional terrain can be seen in the terrigenous hills, limestone mountains and islands, and in caves of different layers. At the bottom of the bay, ancient river branches, remaining karst blocks and especially submerged karst fields are of interest.
Ha Long Bay is a mature karst landscape in hot and humid tropical conditions encroached by the sea. The combination of factors such as thick limestone layers (about 1,000m), hot and humid climate and slow uplifting tectonics with all phases of a modern marine cycle have created a wonderful example of large-scale mature limestone karst, representing a magnificent geological wonder.
It can be said that Ha Long Bay gathers almost all the basic forms of karst terrain such as karst plains, funnels & valleys, and karst peaks & towers. The marine process in the late Pleistocene and in the Holocene directly participated in the karst process in Ha Long with specific products created such as sea ridges, sea frog caves, and tunnel caves. The sea also submerged funnels, sinkholes and karst valleys, creating salt lakes, or pines and aquifers. The cave system in Halong Bay is also diverse, with over 60 known caves belonging to three main groups: ancient underground caves (hanging caves), karst caves, and sea frog caves.
The bay boasts many attractive geological manifestations with high scientific value such as stratigraphic boundaries, fossil sites, blocks, and veins of crystalline minerals in rocks. There are also folds and layers on cliffs, sliding surfaces and breccias representing tectonic faults, karst topography and modern marine topography, erosion ridges, and barnacle traces demonstrating ancient sea levels, etc. All of them are geological heritages that need to be thoroughly studied and protected.
